Channel estimation in conventional Code Division Multiple Access (CDMA) base receivers, such as base receivers within Radio Access Networks (RANs) designed in accordance with 3 Generation (3G) standards such as CDMA 2000 or Interim Standard 2000 (IS2000), Universal Mobile Telecommunication System (UMTS), and the like, is usually performed using a low-pass filter with a fixed bandwidth to establish and maintain communication with a communication unit such as cellular communication unit moving with a user within a mobile platform such as a vehicle traveling at various speeds within the RAN. To perform channel estimation, a bandwidth of, for example, 250 Hz can be used and is generally effective for most normal ambulatory or vehicular speeds.
Channel estimation fails however when the communication unit travels at high speeds. For example when a communication unit is attempting to establish or maintain a link while within a high speed vehicle such as a bullet train, where speeds of as much as around 450 km/h can be reached, the performance degradation can exceed 1 dB for a 2 GHz carrier frequency. In order to address channel estimation associated with communications while traveling at high speeds, the channel estimation bandwidth must be extended. Simply replacing the conventional 250 Hz bandwidth channel estimation filter with a channel estimation filter having an extended bandwidth however, results in a significant performance degradation at normal speed ranges.
Other proposed solutions to extending the bandwidth of the channel estimation filter include the use of adaptive filtering. In some simple adaptive channel estimation procedures, channel estimation filter coefficients may be adjusted according to an estimated speed based on, for example, Doppler estimation, however disadvantages exist in such approaches. By changing filter coefficients, undesirable transient effects are introduced which can disrupt estimation. Moreover, systems using Doppler estimation and other methods have additional disadvantages in that they are undesirably high in complexity.